The Federal Aviation Administration (FAA) requires that obstructions to aircraft navigation, such as towers, cables and tall buildings be fitted with visibly perceivable elements to render these structures highly visible to approaching aircraft. FAA Advisory Circular 150/5345-43 forms a specification of technical requirements for these lights in the United States. Within Advisory Circular 150/5345-43 there exists a requirement for a medium-intensity flashing red obstruction light system, designated the “L-864” and a medium-intensity flashing white obstruction light, designated the “L-865.” These obstruction lights are to be placed in accordance with a set plan at levels on all obstructions that are potential hazards to air navigation.
For the L-864 obstruction light, at all radials throughout a 360 degree azimuth, there must be a peak effective intensity of 2,000±25 percent candela. There must also be a minimum effective intensity of 750 candela throughout a minimum vertical beam spread of 3 degrees. For the L-865 obstruction light, at all radials throughout a 360 degree azimuth, there must be a peak effective intensity of 20,000±25 percent candela during operation at day and twilight conditions, and 2,000±25 percent candela during night conditions. The L-865 obstruction light also includes a minimum vertical beam spread of 3 degrees.
A drawback of these obstruction lights is that they typically utilize incandescent lamps, which have a relatively limited service life. Consequently, the incandescent lamps require frequent replacement. Since the obstruction lights are mounted atop tall structures, replacing these lamps can be inconvenient, time-consuming, expensive and even dangerous. Utilizing light emitting diodes (LEDs) as a light source in obstruction lights overcomes many of these drawbacks. However, LEDs present new design challenges.
Another drawback of conventional obstruction lights is light pollution. Light pollution as it relates to obstruction lighting may be generally defined as the emission of light outside the band specified by Advisory Circular 150/5345-43. Light pollution can be an annoyance, particularly when the obstruction light is proximate to residential areas. In some cases light pollution can cause problems such as sleep deprivation or the blocking of an evening view.
In an optical system for an obstruction light, one approach for arranging LED light sources is to orient them vertically, aimed outwardly from the light assembly. However, shaping multiple light sources into a tight continuous horizontal beam requires a lens, which is less efficient than a reflector. Additionally, the LED junctions thusly configured are more vulnerable to damage due to lightning effects.
Another approach is to mount the LEDs so they are oriented horizontally and aimed upwardly, using a reflector to shape and redirect the light outwardly. In this configuration the reflector is very efficient and also acts as a lightning mediator. Another advantage of this arrangement is that it minimizes direct-light emissions from the LEDs shining downwardly from the obstruction light, which may be considered a neighborhood annoyance.
Orienting LEDs so that they are aimed downwardly is also desirable since it offers more efficient cooling of the LEDs and makes servicing of the LEDs more convenient. However, this arrangement is problematic because it inherently directs some of the LED light toward the neighborhood below the obstruction light.
Moreover, horizontally orienting LEDs and aiming them toward a reflector is undesirable, as this directs the brightest part of the LED beam toward the flatter area of the reflector, thereby reducing beam focus.
In addition to obstruction lights, strobe lights and beacons (hereafter collectively and generally termed “anti-collision lights”) are attached to vehicles, and to obstructions such as buildings and communication towers. Anti-collision lights are designed to warn vehicle operators of hazards to navigation, typically by periodically illuminating the light in a repetitive, attention-getting on-and-off pattern.
Current ground-based anti-collision technology typically comprises high-intensity lights that may be configured to flash at predetermined colors, frequencies, and intensities. Their design is intended to provide a visually perceivable alert to deter potential collisions. These lights have proven effective over time, but they have not significantly changed in almost eight decades. While anti-collision lights have increased in intensity and visibility, become more reliable and energy efficient, and have developed the ability to report their operating condition (i.e., faults) and status, they have not evolved beyond simply flashing or blinking a light at a regular interval to provide a simple warning. Since the light has no active role in collision avoidance, it is incumbent upon the operator of a vehicle in the vicinity of the light to see it, recognize it, and react appropriately to avoid a collision.
As population densities increase, the current anti-collision technology is being stressed. The increasing population density creates three challenges for the existing state-of-the-art flashing anti-collision light. Firstly, there is more traffic and population in a given geographic region, which increases the potential for a collision. Secondly, more people require more infrastructure, which results in more man-made obstacles being erected with which to collide. Finally, current technology is increasingly becoming more dependent upon wireless resources, resulting in an ever-increasing number of transmitting and receiving towers that may become hazards to navigation. Growing populations, expanding infrastructure requirements, and evolving wireless technologies are all resulting in a significant increase in the potential for dangerous collisions while anti-collision technology has effectively remained stagnant.
Furthermore, renewable-energy systems such as wind turbines are becoming increasingly common. These systems, owing to their size, often present potential hazards to air navigation.